(a) Field of the Invention
The present invention relates to a lock mechanism for use on closure members, such as a sliding door, and more particularly to an improved latch type lock mechanism providing visual display of the position of the lock and further providing positive locking to prevent disengagement of the lock, by exterior forces on the lock slide plate, when in the locked position.
(b) Description of Prior Art
Door lock mechanisms of the latch type, to which the present invention relates, are known, such as disclosed in Canadian Pat. No. 963,505 issued on Feb. 25, 1975. That patent is concerned with a door latch assembly for use on sliding doors and providing visual display of the position of the lock, whether in a locked or an unlocked position. Such visual display is provided by displaying one of two color indicias, indicative of the position of the lock, by sliding a lock activating member which covers one of them. A disadvantage of such a lock is that these indicias wear out quickly or become unglued when they are provided as a colored glue tab, and are very small and difficult to see from far away.
Also, such door latch mechanisms, employing sliding locking members, have a disadvantage in that such members can become unlocked by applying a pressure to the door frame along the long axis of the slide locking plate member or otherwise applying a force thereto to displace the slide to cause the lock to become disengaged. Therefore, there exists a need to make sure that such slide locking plate member is positively engaged by the lock mechanism and cannot be unlocked by applying a force thereto along the long axis of the slide member.